A Compression Fitting MTA Brass Elbow is a type of pipe fitting used to connect two pipes or tubes together. It is made of brass and is used in plumbing applications. The MTA stands for Male Threaded Adapter. It has a male threaded end on one side and a compression fitting on the other side. The compression fitting is used to connect the pipe or tube to the adapter. The elbow shape allows for a change in the direction of the pipe or tube.